1. Field of the Invention
The present invention relates to a single-tub washing machine, and more specifically to a fully automatic single-tub washing and dehydrating machine built in with a microcomputer and suitable for eliminating an erroneous operation thereof during dehydration. The invention further relates to a proposal of a new filter unit for use in the fully automatic single-tub washing and dehydrating machine.
2. Description of the Related Art
A typical fully automatic washing and dehydrating machine performs successive steps of water supplying, washing/rinsing (i.e., agitating) and dehydrating to complete a washing operation. In effecting dehydrating operations in the rinsing step and the dehydrating step, initially, the washing water is drained. One of conventional control of the process is described, for example, in Japanese Patent Application Laid-Open Sho 59 No. 44299. In this disclosure, discharge of water is started in a first phase of a draining step, and then when water level sensor detects a predetermined "reset water level", the discharge of water is continued until a predetermined time (for example, 30 seconds) passes away, thereafter the dehydrating step is started.
FIG. 1 is a sectional view showing a construction of such a single-tub washing machine. In the figure, a dehydrated water-receiving tub 142 is elastically supported through a supporting rod 143 and a spring 144 in an external tub 141. A washing/dehydrating tub 145, having dehydration holes 145a in the upper portion thereof, is mounted rotatably in the dehydrated water-receiving tub 142, while a pulsator 146, having a washing impeller 146a on a front side thereof and a pumping impeller 146b on a rear side thereof, is provided rotatably in the bottom center of the washing/dehydrating tub 145.
Reference numeral 154 designates a drain valve, which will be opened when water in the washing/dehydrating tub 145 is discharged outside from the machine through a drain hose 155. A water level sensor, designated at 147, detects pressure in an air trap 156 disposed in the course of a draining path 150 (upstream of drain valve 154) by way of a pipe 148, and sends out a detected signal for a control unit 149, which in turn regulates the drain valve 154. A driving motor designated at 151 drives the washing/dehydrating tub 145 and pulsator 146 via a belt 153 and mechanism portion 152.
Next, operations of each component during dehydration will be described. At dehydration, drain valve 154 is opened in response to the signal outputted from control unit 149, and the washing water is discharged through drain hose 155 in the course of drain path 150. Then, washing/dehydrating tub 145 is spun at a high speed to cause centrifugal force to extract the remaining water. The thus extracted water is discharged through dehydration holes 145a provided in the upper part of tub 145 to dehydrated water-receiving tub 142 and discharged outside the machine through drain hose 155.
Meanwhile, many proposals as to fully automatic washing machines have been presented for preventing vibration and scattering of laundries due to imbalance arising during dehydrating process, the prevention of stack of the dehydration holes with the laundries and the protection of lowering of dehydrating efficiency. One of examples of such proposals that employ3 a dehydration tub with a number of dehydration holes is disclosed in Japanese Patent Publication Hei 2 No. 49116, in which the imbalance of the washing is eliminated by causing the pulsator to make intermittent rotations of not more that one revolution during the drainage in the dehydrating step.
On the other hand, Japanese Patent Publication Sho 61 No. 9878 discloses a method using a dehydrating tub without hole, in which water is discharged from dehydrating clearance between the tub and a balancer disposed at the upper side of the dehydrating tub.
A publication of Japanese Patent Application Laid-Open Sho 54 No. 120958 discloses a method in which water is discharged from dehydration holes disposed in the upper portion of the dehydrating tub.
Of these conventional methods, the above cited Japanese Patent Publication Sho 61 No. 9878, in particular, proposes that the taper angle of the dehydrating tub is effectively set at 30.degree. or less in order to prevent the scattering of the laundries, the stack of water-discharging holes with the washing, the lowering of dehydrating efficiency, etc. In this embodiment, the taper angle is practically set at 2.degree. to 3.degree. in order to improve the dehydrating efficiency. Therefore, an inclination angle of a ridge face of the inner wall in the dehydrating tub is set such that, the following relation is satisfied: EQU the taper angle&lt;the inclination angle.ltoreq.30.degree..
In the above cited Japanese Patent Application Laid-Open Sho 54 No. 120958, if the taper angle is 2.degree. or more, a plurality of holes are provided in upper portion of grooves or in the upper boundary portion of the washing/dehydrating tub. In contrast, when the taper angle is less than 2.degree., there is provided at least one dehydration hole inside each groove in a range of from the bottom to the upper portion of the washing/dehydrating tub and one dehydration hole at the above end of each groove.
A typical dehydrating tub provided with many dehydration holes is generally tapered at a ratio of 1/100 or less.
Generally, a typical automatic washing machine is provided with a filtering device in order to remove dust and lint attached to washed clothes from the washing water. Examples of conventional washing machines provided with a filtering device will be described with reference to respective sectional views.
Referring to FIG. 2, the washing machine is provided with a water tub 131 containing washing water. This machine is operated to perform the washing by turning a pulsator 132 while a pumping impeller 132a provided on the rear side is caused to suck the washing water from water tub 131 through a number of holes provided in a flange 133 as shown in FIG. 2. The thus sucked water is ejected into a lifting path 136 that is defined between an inner tub 134 and a filter cover 135 so that lint and dust are collected by a lint filter 137.
On the other hand, in a single-tub washing machine, which holds washing water only in a washing/dehydrating tub, it is necessary to circulate the washing water in the washing/dehydrating tub in order to collect lint and dust. One example of such means is proposed in Japanese Utility Model Application Laid-Open Sho 55 No. 50638, in which, as shown in FIG. 3, a flow path is defined by a channel 122 provided for a washing/dehydrating tub 121 and a filter 124 extending to the vicinity of the periphery of a pulsator 123. The circulating water is sucked by a pumping impeller 127 via through-holes 125 to collect lint and dust by using a brush-like projection 126 mounted on filter 124 in the flow path.
In the course of the drainage described above, when drain valve 154 is opened to start the dehydration, wet laundry materials, such as clothes to be dehydrated may sometimes be stuck on drain holes 150a that serve as entrances of drain path 150. This causes drain path 150 to be blocked. In such a case, the washing water can not flow through drain path 150 downstream of drain holes 150a and the air remains in drain path 150. At the time, the pressure inside air trap 156 is lowered so that water level sensor 147 erroneously detects the state as a reset water level. With this detection, a microcomputer in the conventional control, directs the operation to advance to the next step. In this case, the operation goes to the dehydrating step in which the dehydrating tub 145 containing the water starts to spin. Since the dehydrating tub 145 can not be rotated at a high speed until the water is completely discharged, the dehydrating efficiency might possibly be lowered to a great extent.
In a case where the wet laundries are offset and in an imbalance condition inside dehydrating tub 145, the tub 145 is caused to vibrates when the dehydration is started (or while dehydrating tub 145 rotates at a low speed) if the water is completely drained out. As a result, an imbalance detecting switch is turned on to execute a corrective process. On the other hand, if the water is not completely discharged, the vibration does not occur due to the water left among the wet laundries when the dehydration is started. However, vibration starts to occur as the water is gradually drained and the rotation of the dehydrating tub is accelerated to an increased speed. As a result, an abnormal vibration may occur. Therefor, in either case, the dehydrating process can not be performed normally.
Moreover, of the above, the prior art single-tub washing machine associated with FIG. 3, in particular, has a drawback that relatively small lint can not be collected due to the construction. In addition, there is another drawback that efficiency of the collection of the lint is decreased when the water level is low (i.e., a small amount of clothes is washed) since through-holes 125 are positioned in relatively higher portions of washing/dehydrating tub 121. Further, the flow path defined by the extension of filter 124 successively extends up to only the vicinity of the outside of pulsator 123. Therefore, water flows of the sucked current and of the ejected current by pulsator 123 collide with one another to decrease a sucking efficiency. Consequently, the efficiency of the collection of the lint is still more worsened.